Echo cancellation and suppression systems and methods therefor are known in the art. A speech transmission oriented system, such as a speech communication system, includes a sound production unit such as a speaker and a sound detection unit such as a microphone. The speaker produces sounds received from a remote source and the microphone detects voice sounds which are provided by the user. It is noted that the microphone also detects sounds from other sources such as noise and sounds, which are produced by the speaker (echo), after traveling through and acoustic path therebetween.
Methods and systems for “emphasizing” the voice portion over the noise and echo are known in the art. The common approaches use adaptive filtering to derive a replica of an echo-signal, which is further subtracted from the microphone signal. As a result, a level of the echo-signal is decreased significantly. Speech communication systems, especially hand-held devices, are limited in their processing and storage resources. This fact forces developers to search for new approaches for robust and high quality echo cancellation and echo suppression methods, which can function within these limited conditions.
In the article by A. Hirano et al. “A noise-robust stochastic gradient algorithm with an adaptive step-size suitable for mobile hands-free telephones”, Proc. ICASST-95, v.5, pp. 1392–1395, 1995, an adaptive step-size algorithm is proposed. The algorithm controls the step size of the standard NLMS method, based on the reference input signal power and the noise power.
U.S. Pat. No. 5,608,804 to Hirano, entitled “Method of and apparatus for identifying a system with adaptive filter” is directed to a method of and an apparatus for estimating characteristics of an unknown system, using an adaptive filter, in an echo canceller. A gradient step size, which is controlled dynamically, is a function of the power of the reference input signal. The gradient step size monotonously increases if the power of the reference input signal is smaller than a threshold and monotonously decreases if the power of the reference input signal is greater than the threshold.
U.S. Pat. No. 5,546,459 to Sih, et al., entitled “Variable block size adaptation algorithm for noise-robust acoustic echo cancellation” is directed to an apparatus for acoustic echo cancellation using an adaptive filter. The apparatus updates coefficients of the adaptive filter using a signal block of length L. The block size is adjusted in response to the instantaneous signal-to-noise ratio.